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<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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<body>
  <script>
    let p = new Promise((resolve,reject) => {
      setTimeout(()=>{
        resolve('OK')
        //reject('Err')
      },1000)
    });

    p.then(value => {
      console.log(111)
      //有且只有一个方式
      return new Promise(() => {});
    }).then(value => {
      console.log(222)
    }).then(value => {
      console.log(333)
    }).catch(reason => {
      console.warn(reason);
    })
  </script>
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